Turnstile antenna



March 3, 1942. J. EPSTEIN 2,2'15,o30

TURNSTILE ANTENNA Filed Oct. 17, 1940 2 Sheets-Sheet 1 16.1. 9 FIG 1 50.25.

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J. EPSTEIN 'TURNSTILE ANTENNA 2 Sheets-Sheet 2 Filed 00+. 17, 1940 Zmnentor Patented Mar. 3, 1942 TURNSTILE ANTENNA Jess Epstein, Westmont, N. 3., assignor to Radio Corporation of America, a corporation of Delaware Application October 17, 1940, Serial No. 361,494

Claims.

This invention relates to turnstile antennas and particularly to a turnstile antenna in which currents of quadrature phase are applied to the radiator elements by a pair of concentric transmission lines.

In U. S. Patent No. 2,086,976 George H. Brown describes a turnstile antenna which is fed by four open lines, each of which apply a current of quadrature phases to the respective radiators. These lines require proper terminations at one end and a suitable coupling and phasing network at the other to avoid the effects of poor matching and to split the phase of the currents from the transmitter or other source.

The present invention, as one of its objects, provides an inexpensive, simplified and preadjustable network for feeding a turnstile antenna by means of a pair of concentric transmission lines. Another object is to provide means whereby a turnstile antenna may be readily adjusted to establish a rotating radio frequency field of circular, or elliptical pattern. Another object is to provide means whereby a turnstile may be adjusted to radiate along a vertical axis a radio frequency field of substantially cylindrical or conical shape. An additional object is to provide improved radiator elements for an antenna whereby the elements may be fed currents of quadrature phase by means including a pair of transmission lines.

The invention will be described by referring to the accompanying drawings in which Fig. 1 is a view, partly in section, of one of the radiator elements and a portion of the mast employed in the improved turnstile antenna of the invention; Figs. 2A and 2B are schematic diagrams explanatory of the operation of the radiator element; Fig. 3 is a schematic diagram of a net- Work for feeding quadrature phase currents to the radiator elements; Figs. 4 and 5 are respectively schematic and vector diagrams explanatory of the feeding network; Figs. 6A and 6B are elevational and end views respectively of the north radiator element; Figs. 6C and 6D are elevational and end views respectively of the east radiator element; Fig. 7 is a schematic diagram of the radiator elements and feeding network of a one bay turnstile; and Fig. 8 is a schematic diagram of a two bay turnstile.

Referring to Fig. 1, an inner rod or tubular conductor I is suitably secured to a mast 3 which may be made of either conductive or insulative material. If insulative material is used, the

several inner rods of each bay of the antenna The inner conductor is 55 are connected together.

concentrically surrounded by a conductive, cylindrical sleeve 5 which is preferably slightly shorter than a quarter wave length and spaced from the mast. The inner end of the sleeve is supported by an insulator I; the outer end includes a preferably adjustable shorting plug 9. The current feed point is indicated by the reference character B; the distance to the plug by L and the sleeve length by A. It should be understood that four such radiator elements are mounted around the mast at intervals. These elements are arranged in the same horizontal plane to form one bay of a turnstile.

The operation of the radiator element will be described by referring to Figs. 2A and 2B. Since the total length A of the outer sleeve is somewhat less than a quarter wave, the radiator element will be slightly capacitive, CA. It will also have some resistance, RA. The distance LP to the shorting plug is chosen so that the inner surface of the sleeve and outer surface of the inner rod is slightly inductive Ls. By properly adjusting the shorting plug the inductive reactance may be made to balance the capacitive reactance. Thus the radiator element may be tuned to parallel resonance and its equivalent resistance at point B may be indicated as Re.

The quadrature phasing network will be described by referring to Figs. 3, 4 and 5. If north radiator N and the east radiator E are connected by a serially connected capacitor C and inductor L and fed at their junction H, the phase of the currents in N will lead that of the currents in E. Furthermore, if at the operating frequency f,

1 Za'fC and 21rfL equals R5, then the currents in N will equal the currents in E and the currents in N will lead by 90, as shown in the right hand portion of Fig. 5.

The south radiator element S and the west radiator element W are fed by a similar network 01, L1. This network is fed at its junction point K. If the currents applied to the terminals H and K are out of phase, then the currents applied to the four radiator elements N, E, S and W will be in quadrature phase as shown in Fig. 5.

The required phasing inductors L and capacitors C may be made of concentric lines. As shown in Figs. 6A, 6B, 6C and 6D theseconcentric lines ll, I3, are attached, respectively, to the north and east radiator elements by soldering, brazing or any suitable means making good electrical contact to the radiator. The capacitor section H is made by leaving the inner conductor l5 free; the inductor section I3 is made by shorting the inner conductor I1. It should be understood that the concentric lines ll, l3 add to the radiator elements some capacity which parallels the capacity of the elements and requires a slight modification thereof. The preferred method of adjustment is to attach the lines I I, I3 before adjusting the radiator element. The same type of concentric lines are attached to the south and west radiators S and W to feed these elements.

While the radiator elements may be made so that their equivalent resistance Re is anything over 35 ohms, it is desirable to make the equivalent resistance a function of the number of bays employed. In this manner the impedances may be matched as hereinafter described. First, assuming that the effective length of each element is a quarter wave and therefore its equivalent resistance is 35 ohms, the pair of concentric transmission lines for applying the quadrature phase currents may be arranged as shown in Fig. '7.

The terminal or junction points H and K are connected to a pair of standard '70 ohm concentric lines l1, [9 which are connected together so that their combined length equals a full wave length. Each branch of these lines has an impedance of 140 ohms at a point P three quarters wave length from one terminal K and one quarter wave length from the other terminal. The resultant impedance will be '70 ohms. Therefore, a 70 ohm concentric line may be connected between the point P and the transmitter or power source. Since K is a half wave length further from P than H is from P, it follows that the potential at K will always be opposite the potential at H.

The foregoing coupling and transmission line network was chosen for a single bay and for radiator elements having an equivalent resistance of 35 ohms. In matching two lines to the elements of a plurality of bays, the equivalent resistance Re of the radiator elements may be chosen as follows:

E quivalent Number of bay resistance It should be understood that the bays are effectively spaced a half wave length and the two concentric feed lines are twisted around the mast as shown in Fig. 8. The twisting assures that the currents in the corresponding elements of the several bays will be cophased. By way of example, for six bays each radiator element will have an equivalent resistance of 210 ohms, an antenna length A of about 0.l'7 and a length LP of about 0.155%. When connected together by the transmission lines, the resulting impedance will be 35 ohms. Therefore, the terminating and coupling network of Fig. 7 may be used.

Thus the invention has been described as an improved turnstile in which the radiator elements are tuned to resonance. Adjacent pairs of radiators are connected to phase splitters which each consist of two serially connected transmission line sections having capacitive reactance and inductive reactance. The junctions of the serially connected phase splitter lines are each connected to concentric transmission lines. The termination includes a full wave line, tapped at a quarter wave point, and matched to a conventional line to the transmitter.

It should be understood that the antenna may be used to establish a conical field extending upwardly from the antenna by employing a pair of transmission lines which do not spiral around the mast between adjacent bays. Thus connected the adjacent north radiators are fed in phase opposition and the energy from a six bay turnstile is directed straight up.

If an elliptical field pattern is preferred to the horizontal vertical pattern, it is only necessary to change the ratio of the currents in the four radiator elements from unity to any desired ratio. For example, to make the field in the easterly direction M times the field in the northerly direction, the current in the north radiator is made M times the current in the east radiator. This is accomplished by adjusting C and L to satisfy the equations I claim as my invention:

1. A turnstile antenna including supporting means, four radiator elements located in the same plane and attached at intervals to said supporting means, two phase splitting circuits connected between adjacent radiator elements to apply currents of quadrature phase to said radiator elements, and a pair of transmission lines for applying currents of opposite phase to said phase splitting circuits.

2. A turnstile antenna including supporting means, four radiator elements located in the same horizontal plane and attached at 90 intervals to said supporting means, two phase splitting circuits connected respectively between adjacent pairs of radiator elements to apply quadrature phase currents to said radiator elements, and a pair of transmission lines for applying currents of opposite phase to said phase splitting circuits.

3. A turnstile antenna including supporting means, four radiator elements located in the same horizontal plane and attached at 90 intervals to said supporting means, two phase splitting circuits connected respectively between adjacent pairs of radiator elements to apply quadrature phase currents to said radiator elements, and a full wave concentric transmission line having its terminals connected to said pairs of phase splitting circuits and having a third terminal three quarters of a wave length distant from one of said phase splitting circuits and a quarter wave distant from the other of said phase splitting circuits so that currents of opposite phase may be applied to said phase splitting circuits from a source connected to said third terminal.

4. A turnstile antenna including supporting means, four radiator elements located in the same plane and attached at 90 intervals to said supporting means, said elements each including an inner conductor member and an outer conductor sleeve, means for adjusting the effective lengths of said elements to obtain in each radiator element parallel resonance at the operating frequency, a pair of phase splitting circuits connected respectively between adjacent pairs of radiator elements to apply quadrature phase currents to said radiator elements, and a pair of transmission lines for applying currents of opposite phase to said phase splitting circuits.

5. A turnstile antenna including supporting means, four radiator elements located in the same plane and attached at 90 intervals to said supporting means, said elements each including an inner conductor member and an outer conductor sleeve, means for adjusting the efiective lengths of said elements to obtain in each radiator element parallel resonance at the operating frequency, a pair of phase splitting circuits connected respectively between adjacent pairs of radiator elements to apply quadrature phase currents to said radiator elements, and a full wave concentric transmission line having its terminals connected to said pairs of phase splitting circuits and having a third terminal three quarters of a Wave length distant from one of said phase splitting circuits and a quarter wave distant from the other of said phase splitting circuits so that currents of opposite phase may be applied to said phase splitting circuits from a source connected to said third terminal.

6. A turnstile antenna including supporting means, four radiator elements located in the same plane and attached at 90 intervals to said supporting means, each of said elements including an inner conductor member and an outer conductive sleeve, means for adjusting the efiective lengths of said elements to obtain parallel resonance at the operating frequency, a concentric line conductively secured to each of said elements and having effective lengths such that adjacent lines have reactances of opposite sign, means serially connecting said adjacent lines to apply currents of quadrature phase to said radiator elements, and means for applying currents of opposite phase to the junctions of said serially connected lines.

7. A turnstile antenna including supporting means, four radiator elements located in the same horizontal plane and attached at 90 intervals to said supporting means, each of said elements including an inner conductor member and an outer conductive sleeve, means for adjusting the effective lengths of said elements to obtain in each of said radiator elements parallel resonance at the operating frequency, a concentric line conductively secured to each of said elements, aligned longitudinally therewith, and having effective lengths such that adjacent lines have reactances of opposite sign, means serially connecting said adjacent lines to apply currents of quadrature phase to said radiator elements, and means for applying currents of opposite phase to the junctions of said serially connected lines.

8. A turnstile antenna including a mast, a plurality of bays of radiator elements, each of said bays including four radiator elements located at intervals about said mast, the corresponding elements of each bay being located in the same vertical plane, each of said bays including two phase splitting circuits connected respectively between adjacent pairs of radiator elements to apply currents of quadrature phase to said radiator elements, and means for applying currents of opposite phase to the phase splitting circuits of each bay and currents of the opposite phase to the phase splitting circuit connected to diagonally opposed radiator elements of the next adjacent bay.

9. A turnstile antenna including a mast, a plurality of bays spaced effectively at half wave intervals of radiator elements, each of said bays including four radiator elements located at 90 intervals about said mast, the corresponding elements of each bay being located in the same vertical plane, each of said bays including two phase splitting circuits connected respectively between adjacent pairs of radiator elements to apply currents of quadrature phase to said radiator elements, and means for applying currents of opposite phase to the phase splitting circuits of each bay and currents of the opposite phase to the phase splitting circuit connected to diagonally opposed radiator elements of the next adjacent bay.

10. A turnstile antenna including a mast, a plurality of bays spaced elfectively at half wave intervals of radiator elements, each of said bays including four radiator elements located at 90 intervals about said mast, the corresponding elements of each bay being located in the same vertical plane, each of said bays including two phase splitting circuits connected respectively between adjacent pairs of radiator elements to apply currents of quadrature phase to said radiator elements, and means for applying currents of opposite phase to the phase splitting circuits of each bay and currents of the same phase to the phase splitting circuit connected to diagonally opposed radiator elements of the next adjacent bay.

JESS EPSTEIN. 

